In high-speed printing presses, an imprinted paper web is often dried, by the application of heat, in order to set the printing ink and to prevent the smearing of otherwise possibly insufficiently dried ink on rollers over which the imprinted web is guided. However, this treatment results not only in the desired drying of the paper surface, but also causes a loss of moisture in the composite material of the paper. This loss of moisture can lead to deformation or to formation of waves in the paper, which detracts considerably from the appearance and the useful value of the finished printed product. For the prevention of such deformations, it is known to conduct a heat-dried paper web through a re-moistening installation, in which the lost moisture is again supplied. This re-supply of moisture is done with the aid of moistening devices in the form of arrays of spray nozzles, which spray nozzles distribute a fine fog of a water-silicon emulsion on the front and back of the web.
The addition of silicon oil to the water has a number of advantages, among which are an increase in the surface quality of the web, and therefore a reduced friction between the web and guide rollers and formers; and reduced smearing and smear deposition on formers and the folding apparatus, and the like. The extent to which these advantages can be gained depends on the concentration of the silicon oil in the emulsion. The usual practice is to adapt this concentration of silicon oil in the emulsion to such a degree that the above-mentioned advantages can be obtained to the highest possible degree. However, smearing and the deposition of smears cannot completely be prevented. Soiling of the guide rollers of a folding apparatus, on which the moistened web is processed following re-moistening, can be observed even with a carefully optimized additive concentration of silicon oil in the emulsion.
DE 44 05 332 A1 describes a re-moistening system in the cooling roller stand of a web-fed offset printing press. A plurality of moistening devices are assigned to each side of a web.
DE 199 20 091 A1 discloses a re-moistening liquid which includes silicon.